<VV> Cam shaft bearing wear in the block

[by way of Harry Jensen <hljensen at comcast.net>]

Smitty Smith has it right.  I discovered this problem in the late 70's when 
I rebuilt my first Corvair engine.  The engine ran great except it had a 
strange noise in it.  Using a small hose stuck in my ear and running the 
open end around the engine like a stethoscope I found  that at the rear of 
the engine it sounded as if some one was in there pounding with a hammer.

An engine teardown revealed that the rear cam gearing bore in the block was 
0.010 inch diameter over size.  In those days we all had spare blocks to 
chose from.  I stressed this problem to members in our club and found that 
one member, Frank Davies, had overhauled over fifty engines and had never 
measured the cam bearing bores. Also found many other Corvair owners that 
had never measured these bearings a teardown.  I have measured  a large 
number of blocks and find that the rear bearing  is the one most 
susceptible to excessive wear. The center bearings both have shared loads 
with the other bearings. The bearing at the gear end is larger and subject 
to less rear.  However, all the bearings will wear out of limits if run 
long enough..

Also, the supply of spare engine blocks will not last for ever so we need a 
good fix soon. I have considered inserts similar to those used for the main 
bearings but there is so little metal between the bore and the holes for 
the block half clamping bolts that it may not be possible. An Idea that I 
have pursued but not finished is this:

A variety of hard inner race bearing sleeves are available in the needle 
bearing manufacturers catalogs. Select a race with an outer diameter over 
what would be needed to match the oversized bore in the block rear bearing 
only. Then turn the cam shaft rear bearing down for a high press fit and 
press the sleeve on the cam.  Then take the shaft to a shop and have the 
sleeve ground to the correct size.  This would only  work for the rear 
bearing. For all of the bearings have the Corvair parts suppliers have cams 
made with a high oversize bearing OD's and then have them ground to fit the 
block.

There is room for many ideas and we need to pursue the answer to this 
problem now not later. Smitty said it right!

Tom Silvey